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41.
Combined in-situ SAXS/WAXS and HRTEM study on crystallization of (Cu60Co40)1 − xZrx metallic glasses
CuZr as well as CoZr are well known metallic glass-formers in a wide compositional range. Since the binary Cu-Co system exhibits a metastable liquid-liquid miscibility gap, i.e. Cu and Co tend to separate from each other, the ternary Cu-Co-Zr system is a promising candidate to form phase separated glass-glass composites. In this work (Cu60Co40)1 − xZrx metallic glasses with relatively low Zr contents of x = 37 and x = 32 were prepared by melt spinning and investigated by in-situ small-angle and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). Certain heat treated samples were additionally investigated by high-resolution transmission electron microscopy (HRTEM). Even for x = 32 there are no indications for any kind of phase separation in the as-quenched state within experimental resolution, i.e. the critical temperature Tc for a liquid-liquid phase separation has already decreased from 1556 K for binary Cu60Co40 to a temperature below the glass transition temperature Tg = 762(5)K found for (Cu60Co40)68Zr32. Combined in-situ SAXS/WAXS and HRTEM investigations reveal that thermal annealing also does not induce an amorphous-amorphous phase separation. Instead the formation of nano crystallites of a so far unknown Cu-rich/Zr-poor phase with relatively low activation energy for crystallization Ea = 116(7) kJ/mol at temperatures far below the crystallization temperature deduced from DSC measurements is observed. 相似文献
42.
A new Li-Al-N-H system for reversible hydrogen storage 总被引:2,自引:0,他引:2
Complex metal hydrides are considered as a class of candidate materials for hydrogen storage. Lithium-based complex hydrides including lithium alanates (LiAlH(4) and Li(3)AlH(6)) are among the most promising materials owing to its high hydrogen content. In the present work, we investigated dehydrogenation/rehydrogenation reactions of a combined system of Li(3)AlH(6) and LiNH(2). Thermogravimetric analysis (TGA) of Li(3)AlH(6)/3LiNH(2)/4 wt % TiCl(3)-(1)/(3)AlCl(3) mixtures indicated that a large amount of hydrogen (approximately 7.1 wt %) can be released between 150 degrees C and 300 degrees C under a heating rate of 5 degrees C/min in two dehydrogenation reaction steps. The results also show that the dehydrogenation reaction of the new material system is nearly 100% reversible under 2000 psi pressure hydrogen at 300 degrees C. Further, a short-cycle experiment has demonstrated that the new combined material system of alanates and amides can maintain its hydrogen storage capacity upon cycling of the dehydrogenation/rehydrogenation reactions. 相似文献
43.
In Korea, many forms of credit guarantees have been issued to fund small and medium enterprises (SMEs) with a high degree of growth potential in technology. However, a high default rate among funded SMEs has been reported. In order to effectively manage such governmental funds, it is important to develop an accurate scoring model for selecting promising SMEs. This paper provides a support vector machines (SVM) model to predict the default of funded SMEs, considering various input variables such as financial ratios, economic indicators, and technology evaluation factors. The results show that the accuracy performance of the SVM model is better than that of back-propagation neural networks (BPNs) and logistic regression. It is expected that the proposed model can be applied to a wide range of technology evaluation and loan or investment decisions for technology-based SMEs. 相似文献
44.
Jing-wen Li Zhi-wen Wang Jaeun Lee Moo Young Sohn Zhong-fu Zhang En-qiang Zhu 《应用数学学报(英文版)》2010,26(3):525-528
In this paper we get some relations between α(G), α'(G), β(G), β'(G) and αT(G), βT(G). And all bounds in these relations are best possible, where α(G), α'(G),/3(G), β(G), αT(G) and βT(G) are the covering number, edge-covering number, independent number, edge-independent number (or matching number), total covering number and total independent number, respectively. 相似文献
45.
This study develops a new electromechanical (EM) impedance measurement technique specifically for continuous monitoring of large structures. Conventionally, a single surface-mounted lead zirconate titanate (PZT) transducer is often used to measure the EM impedance of a coupled PZT-structure system for damage diagnosis. However, when the target structure is massive, the impedance measurement becomes challenging. In this study, a dual piezoelectric transducer, composed of two separate but concentric PZT segments, is used for effective measurement of the EM impedance from large-scale structures. The impedance measurement using the dual PZT is theoretically formulated and numerically verified. Then, a series of experiments are carried out on a laboratory-size specimen and full-scale bridge and building structures. The experimental results reveal that the proposed technique successfully measures the EM impedance signals from massive structures with a high signal-to-noise ratio (SNR) and good repeatability even when the conventional techniques fail to do so. At the same time, the proposed technique allows low-cost and fast measurement of impedance signals. 相似文献
46.
Jongho Shin Kyungsik Jang Ki-Soo Lim Ik-Bu Sohn Young-Chul Noh Jongmin Lee 《Applied Physics A: Materials Science & Processing》2008,93(4):1015-927
We report the spectroscopic properties of femtosecond laser-irradiated sodium-alumino-borate glass doped with silver and gold
ions. We precipitated gold and silver nanoparticles by laser irradiation and annealing at 400°C for 30 min. The irradiation
and annealing treatment produced different absorption and emission characteristics in Au3+ doped and Au3+, Ag+ codoped glasses, and the possible mechanisms of the observed results are discussed. The size of the nanoparticles was estimated
by TEM and absorption band analysis. 相似文献
47.
AbstractIn the course of our continuing investigation of bioactive secondary metabolites from marine-derived fungal strains, a racemate of a novel diphenolic derivative named (±)-tylopilusin D (1) along with ten previously known secondary metabolites (2–11) were isolated from a marine-derived fungal strain Aspergillus sp. SF-5929. Their structures were elucidated mainly by analysis of NMR and MS data. In addition, the inhibitory effects of the isolated compounds against protein tyrosine phosphatase 1B (PTP1B) activity were evaluated, and compounds 1, 2, and 5–7 inhibited PTP1B activity with IC50 values ranging from 3.3 to 8.1?µM. Kinetics studies suggested that compounds 1, 2, and 5 had noncompetitive inhibitory effects against PTP1B. 相似文献
48.
Decarboxylative CC cross-couplings of 2-aminopyrimidine-5-carboxylic acids under a Pd/Ag-based catalytic system opens a new platform for the introduction of diverse C5 substituents. The reaction methods proceeded efficiently with a wide range of the acids and the coupling partners of aryl iodides, alkenes, bromoalkynes, and azoles. Considering ready availability of 2-aminopyrimidine-5-carboxylic acid from the oxidative dehydrosulfurative CN cross-coupling of the 3,4-dihydropyrimidin-1H-2-thiones, this reaction method unambiguously pave a shortcut to densely substituted 2-aminopyrimidine derivatives with unprecedented diversity. 相似文献
49.
A genetic algorithm was employed in association with high-throughput synthesis and characterization in an attempt to search for red phosphors with high photoluminescent intensity. A tetravalent manganese-doped alkali earth germanium oxide system, with an emission color close to a desirable deep red, was screened with the assistance of a genetic algorithm to pinpoint the phosphor exhibiting the highest photoluminescence. As the genetic algorithm was in progress, the PL intensity increased and maximized in the fourth generation. The highest and the average PL intensity of the fourth generation improved by 23 and 120%, respectively, compared with that of the first generation. 相似文献
50.
A new cyclic depsipeptide stereocalpin A (1) has been isolated from the MeOH extract of the Antarctic lichen Stereocaulon alpinum by various chromatographic methods. The structure of stereocalpin A (1) was mainly determined by analysis of the NMR spectroscopic data and by chemical methods. Stereocalpin A (1) is a unique cyclic peptide incorporating an unprecedented 5-hydroxy-2,4-dimethyl-3-oxo-octanoic acid in the structure. Stereocalpin A (1) shows moderate cytotoxicity against three human solid tumor cell lines. 相似文献